The field of the invention relates to ankle, foot, and lower leg prosthetic devices. In particular, the field of the invention relates to passive ankle, foot, and lower leg prosthetic devices.
Prosthetic ankle and foot devices have been described. (See U.S. Pat. Nos. 7,955,399; 7,862,622; 7,819,926; 7,648,533; 7,611,543; 7,578,852; 7,101,403; 6,942,704; 6,929,665; 6,436,149; 6,280,479; 6,206,934; 6,071,313; 5,913,901; 5,728,175; 5,593,455; 5,571,212; 5,509,936; 5,486,209; 5,425,781; 5,425,780; 5,405,411; 5,181,932; 5,156,630; 5,066,305; 4,764,172; 4,645,509; 4,605,417; 4,547,913; 4,442,554; and 4,370,761; and U.S. Published Patent Application Nos. 20110257764; 20110106274; 20090319055; 20090281638; 20090265018; 20080281436; 20080262635; 20080228288; 20080188950; 20080033579; 20070299544; 20070219643; 20070213841; 20060178754; 20060064176; 20050267601; 20050203640; 20050049721; 20050038525; 20050033451; 20050033450; 20040236435; 20040225375; 20040186590; 20030105531; and 20020143407; the contents of which are incorporated herein by reference in their entireties).
Current commercially available prosthetic ankles/feet are based on passive leaf springs that absorb and release energy during walking. These springs reduce the impact of ground reaction forces that occur during walking and convert some of the absorbed energy into energy used to propel the body forward. The energy stored, however, is significantly less than that required to propel the body forward during push-off. Amputees that use these existing passive devices tend to walk more slowly and expend more energy than normal walkers. To obtain the desired mechanical characteristics, the ankle joint must display active properties. More energy must be extracted from the ankle than was provided in ankle deflection.
Current research in prosthetic ankle design addresses the need for more energy during push-off to propel the body forward. Most current research is directed at bionic ankles in which active components (motors) are used to assist in propelling the body forward. The limitations of these active (or bionic) designs are the increased size and weight of the ankle. The degree to which size and weight increases is roughly determined by the amount of power provided by the actuator to propel the body forward. In order to minimize the increased size and weight, a good prosthesis design is one for which the majority of the desired behavior is obtained using passive elements and only a limited contribution is required of the motors.
The present inventors are unaware of any report in which active behavior using only passive components has been achieved in a prosthetic ankle design. Typically, prior passive designs do not simulate natural ankle mechanical characteristics. Furthermore, prior active designs require large, heavy actuators to achieve similar mechanical characteristics. The presently disclosed devices do not need sensors or actuators to achieve the active behavior associated with normal walking.